SUMMARY OF THE INVENTION
In one form, the invention comprises a valve comprising first, second and third orifices and means controlling the cross-section of fluid flow between said first and second and said first and third orifices, said means comprising a first cylinder mounted for rotation about its axis and having its periphery in contact with a first sealing surface at a region between the first and second orifices, a second cylinder mounted for rotation about its axis and having its periphery in contact with a second sealing surface at a region between the first and third orifices, each cylinder having a circumferentially extending groove formed in its periphery, the depth of which groove increases from one end of the groove to a point of maximum depth and decreases from said point of maximum depth to the other end of the groove.
In another form, the invention comprises a valve comprising first, second and third orifices and means controlling the cross-section of fluid flow between said first and second and said first and third orifices, said means comprising a first cylinder mounted for rotation about its axis, and having its periphery in contact with a first sealing surface at a region between the first and second orifices, a second cylinder mounted for rotation about its axis and having its circumferential surface in contact with a second sealing surface at a region between the first and third orifices, each cylinder having a circumferentially extending groove formed in its periphery, the depth of which groove increases from one end of the groove to a point of maximum depth and decreases from said point of maximum depth to the other end of the groove.
Preferably, each of the sealing surfaces comprises the periphery of a cylinder mounted for rotation with the cylinder with which it co-operates. In preferred forms therefore, the invention comprises a valve comprising first, second and third orifices and means controlling the cross-section of fluid flow between said first and second and said first and third orifices, said means comprising a first cylinder mounted for rotation about its axis, a second cylinder mounted for rotation about its axis and having its periphery in contact with that of the first cylinder at a region between the first and second orifices, a third cylinder mounted for rotation about its axis and having its periphery in contact with that of the first cylinder at a region between the first and third orifices, said axes being parallel, at least the first cylinder or each of the second and third cylinders having a circumferentially extending groove formed in its periphery.
In preferred forms, each of the cylinders is provided with a circumferentially extending groove, the groove depth in each case increasing from one end of the groove to a point of maximum depth and decreasing from that point to the other end of the groove, and the grooves are so contoured and orientated that they form a pair of apertures controlling the fluid flow, such that one aperture decreases in cross-section as the other aperture increases, and vice versa.